Ghrelin--a new player in glucose homeostasis?

The Regulation of Metabolic Homeostasis by Incretins and the Metabolic Hormones Produced by Pancreatic Islets

In healthy humans, the complex biochemical interplay between organs maintains metabolic homeostasis and pathological alterations in this process result in impaired metabolic homeostasis, causing metabolic diseases such as diabetes and obesity, which are major global healthcare burdens. The great advancements made during the last century in understanding both metabolic disease phenotypes and the regulation of metabolic homeostasis in healthy individuals have yielded new therapeutic options for diseases like type 2 diabetes (T2D). However, it is unlikely that highly desirable more efficacious treatments will be developed for metabolic disorders until the complex systemic regulation of metabolic homeostasis becomes more intricately understood. Hormones produced by pancreatic islet beta-cells (insulin) and alpha-cells (glucagon) are pivotal for maintaining metabolic homeostasis; the activity of insulin and glucagon are reciprocally correlated to achieve strict control of glucose levels (normoglycaemia). Metabolic hormones produced by other pancreatic islet cells and incretins produced by the gut are also crucial for maintaining metabolic homeostasis. Recent studies highlighted the incomplete understanding of metabolic hormonal synergism and, therefore, further elucidation of this will likely lead to more efficacious treatments for diseases such as T2D. The objective of this review is to summarise the systemic actions of the incretins and the metabolic hormones produced by the pancreatic islets and their interactions with their respective receptors.

Bifidobacterium longum counters the effects of obesity: Partial successful translation from rodent to human

Background

The human gut microbiota has emerged as a key factor in the development of obesity. Certain probiotic strains have shown anti-obesity effects. The objective of this study was to investigate whether Bifidobacterium longum APC1472 has anti-obesity effects in high-fat diet (HFD)-induced obese mice and whether B. longum APC1472 supplementation reduces body-mass index (BMI) in healthy overweight/obese individuals as the primary outcome. B. longum APC1472 effects on waist-to-hip ratio (W/H ratio) and on obesity-associated plasma biomarkers were analysed as secondary outcomes.

Methods

B. longum APC1472 was administered to HFD-fed C57BL/6 mice in drinking water for 16 weeks. In the human intervention trial, participants received B. longum APC1472 or placebo supplementation for 12 weeks, during which primary and secondary outcomes were measured at the beginning and end of the intervention.

Findings

B. longum APC1472 supplementation was associated with decreased bodyweight, fat depots accumulation and increased glucose tolerance in HFD-fed mice. While, in healthy overweight/obese adults, the supplementation of B. longum APC1472 strain did not change primary outcomes of BMI (0.03, 95% CI [-0.4, 0.3]) or W/H ratio (0.003, 95% CI [-0.01, 0.01]), a positive effect on the secondary outcome of fasting blood glucose levels was found (-0.299, 95% CI [-0.44, -0.09]).

Interpretation

This study shows a positive translational effect of B. longum APC1472 on fasting blood glucose from a preclinical mouse model of obesity to a human intervention study in otherwise healthy overweight and obese individuals. This highlights the promising potential of B. longum APC1472 to be developed as a valuable supplement in reducing specific markers of obesity.

Funding

This research was funded in part by Science Foundation Ireland in the form of a Research Centre grant (SFI/12/RC/2273) to APC Microbiome Ireland and by a research grant from Cremo S.A.

The neurological effects of ghrelin in brain diseases: Beyond metabolic functions

Ghrelin, a peptide released by the stomach that plays a major role in regulating energy metabolism, has recently been shown to have effects on neurobiological behaviors. Ghrelin enhances neuronal survival by reducing apoptosis, alleviating inflammation and oxidative stress, and accordingly improving mitochondrial function. Ghrelin also stimulates the proliferation, differentiation and migration of neural stem/progenitor cells (NS/PCs). Additionally, the ghrelin is benefit for the recovery of memory, mood and cognitive dysfunction after stroke or traumatic brain injury. Because of its neuroprotective and neurogenic roles, ghrelin may be used as a therapeutic agent in the brain to combat neurodegenerative disease. In this review, we highlight the pre-clinical evidence and the proposed mechanisms underlying the role of ghrelin in physiological and pathological brain function.

Changes in ghrelin and asymmetrical dimethylarginine in obese Mexican adolescents after six-month lifestyle intervention

The aim of this study was to evaluate the effect of a six-month lifestyle intervention on ghrelin and asymmetrical dimethylarginine (ADMA) in obese Mexican adolescents. A total of 65 obese Mexican adolescents aged 10-16 years completed a six-month lifestyle intervention. Anthropometric and biochemical parameters were assessed at baseline and at six months. Twenty normal-weight adolescents were also evaluated at baseline. Insulin resistance (IR) was determined by the homeostasis model assessment of IR (HOMA-IR). Ghrelin and ADMA were determined by enzyme-linked immunosorbent assay. Obese adolescents presented significantly higher triglycerides, cholesterol, glucose, insulin, HOMA-IR, and ADMA levels, while ghrelin was significantly lower. The lifestyle intervention led to a significant improvement in HOMA-IR, ghrelin, and ADMA in the whole studied obese subjects. ADMA and ghrelin levels were associated with BMI and IR components. According to the value of HOMA-IR, the obese subjects were divided into subjects with or without IR, no difference in ghrelin and ADMA was observed in these two subgroups. After intervention, the obese with IR showed increased ghrelin and decreased ADMA, while the obese without IR only showed improvement in ghrelin. The multiple linear regression analysis revealed that the changes of systolic blood pressure were the only predictor for the changes of ghrelin in the obese with IR. Our study demonstrated the increase of ADMA and the decrease of ghrelin in obese adolescents. Lifestyle intervention improved insulin resistance, decreased ADMA, and increased ghrelin in obese subjects with IR although no significant weight loss was observed.

Ghrelin suppresses glucose-stimulated insulin secretion and deteriorates glucose tolerance in healthy humans

OBJECTIVE

The orexigenic gut hormone ghrelin and its receptor are present in pancreatic islets. Although ghrelin reduces insulin secretion in rodents, its effect on insulin secretion in humans has not been established. The goal of this study was to test the hypothesis that circulating ghrelin suppresses glucose-stimulated insulin secretion in healthy subjects.

RESEARCH DESIGN AND METHODS

Ghrelin (0.3, 0.9 and 1.5 nmol/kg/h) or saline was infused for more than 65 min in 12 healthy patients (8 male/4 female) on 4 separate occasions in a counterbalanced fashion. An intravenous glucose tolerance test was performed during steady state plasma ghrelin levels. The acute insulin response to intravenous glucose (AIRg) was calculated from plasma insulin concentrations between 2 and 10 min after the glucose bolus. Intravenous glucose tolerance was measured as the glucose disappearance constant (Kg) from 10 to 30 min.

RESULTS

The three ghrelin infusions raised plasma total ghrelin concentrations to 4-, 15-, and 23-fold above the fasting level, respectively. Ghrelin infusion did not alter fasting plasma insulin or glucose, but compared with saline, the 0.3, 0.9, and 1.5 nmol/kg/h doses decreased AIRg (2,152 +/- 448 vs. 1,478 +/- 2,889, 1,419 +/- 275, and 1,120 +/- 174 pmol/l) and Kg (0.3 and 1.5 nmol/kg/h doses only) significantly (P < 0.05 for all). Ghrelin infusion raised plasma growth hormone and serum cortisol concentrations significantly (P < 0.001 for both), but had no effect on glucagon, epinephrine, or norepinephrine levels (P = 0.44, 0.74, and 0.48, respectively).

CONCLUSIONS

This is a robust proof-of-concept study showing that exogenous ghrelin reduces glucose-stimulated insulin secretion and glucose disappearance in healthy humans. Our findings raise the possibility that endogenous ghrelin has a role in physiologic insulin secretion, and that ghrelin antagonists could improve beta-cell function.

Short- and long-term relationships of serum ghrelin with changes in body composition and the metabolic syndrome in prepubescent obese children following two different weight loss programmes

OBJECTIVES

Ghrelin has been proposed to be a regulator of energy balance, and its dysregulation may be important in obesity. The aims of this study were (i) to compare short- and long-term changes in circulating ghrelin concentration after increasing energy expenditure vs. its changes after decreasing energy intake, (ii) to determine factors associated with changes in ghrelin level, and (iii) to assess relationships of ghrelin concentration with metabolic syndrome (MetS) in prepubescent obese children.

DESIGN

Randomized controlled trial.

PATIENTS

About 100 obese children aged 7-9 years.

MEASUREMENTS

After baseline testing, children were randomly assigned to two interventional groups, either receiving dietary recommendations or engaging in physical training classes for 6 months. Ghrelin, insulin, leptin, fasting blood sugar, lipid profile and anthropometric indexes, as well as energy intake and expenditure were measured.

RESULTS

Of the participants, 92 completed the 6-month trial, and 87 returned for the 1-year follow-up. Except ghrelin level, other biochemical variables had no significant change at 12- vs. 6-month follow-up. In both groups, ghrelin showed a progressive increase in the periods of time with significant reduction of overweight and negative energy balance; while after the end of the trial, when children regained weight, it decreased toward baseline levels. Baseline ghrelin had strong negative correlation with measures of central obesity. The odds of having the MetS were 12% lower in the middle and 37% lower in the highest tertile of ghrelin level. As the number of MetS components increased, there was a progressive decrease in ghrelin and quantitative insulin sensitivity check index (QUICKI), with a progressive increase in serum insulin, HOMA-R and leptin levels.

CONCLUSIONS

Ghrelin increases in response to overweight reduction and negative energy balance resulting from either an exercise intervention or reduction in food intake in prepubescent obese children. It is unlikely to regulate long-term energy balance in young obese children.

Ghrelin and obestatin levels in severely obese women before and after weight loss after Roux-en-Y gastric bypass surgery

BACKGROUND

Ghrelin and obestatin are derived from the same gene but have different effects: Ghrelin stimulates appetite, and previous-albeit inconsistent-data show that obestatin may be involved in satiety. The present study was designed to test the hypothesis that Roux-en-Y gastric bypass (RYGB) surgery and/or the weight loss that reliably results from this procedure would alter levels of ghrelin and obestatin and ghrelin/obestatin ratios in a cohort of morbidly obese women.

METHODS

This is a longitudinal follow-up study in 18 morbidly obese women (mean weight 131.2 kg, mean body mass index [BMI] 47.4). Clinical parameters and fasting serum concentrations of ghrelin, obestatin, triglycerides, low-density lipoprotein cholesterol, glucose, and insulin were measured before and 2 years after RYGB surgery, which was associated with body weight reductions of 41.5 +/- 11.6 kg (mean 62.5% excess weight loss).

RESULTS

Ghrelin concentrations (-12%, p = 0.022) and ghrelin/obestatin ratios (-14%, p = 0.017) were lower after surgery than before, while obestatin levels did not change. Changes in ghrelin concentrations correlated with changes in insulin levels (r = 0.45, p = 0.011). Most cardiovascular risk factors studied improved postsurgically (p < 0.01).

CONCLUSION

In contrast to previous weight loss studies involving gastric banding, ghrelin levels decreased and obestatin levels remained stable after massive weight loss in long-term follow-up. The favorable gastrointestinal hormone profiles observed are likely to contribute to the long-term weight loss success rate attributed to RYGB.

Obestatin and ghrelin levels in obese children and adolescents before and after reduction of overweight

OBJECTIVES

Obestatin and ghrelin, which are derived from the same gene, are observed to have opposite effects on weight status. The aims of this study were to compare obestatin concentrations in obese and normal-weight children and to analyse the effect of weight loss on obestatin and ghrelin levels.

METHODS

We examined anthropometrical markers and fasting serum obestatin, ghrelin, leptin, glucose and insulin concentrations in 44 obese children (mean age 11.2 years) before and after participating in a 1-year outpatient obesity intervention programme based on a high-carbohydrate, fat-reduced diet and increased physical activity. Additionally, total ghrelin, obestatin and leptin levels were determined in 22 normal-weight healthy children of similar age, gender and pubertal stage.

RESULTS

Obestatin and leptin concentrations were significantly (P < 0.001) higher and ghrelin concentrations were significantly (P < 0.001) lower in obese children compared to nonobese children. In contrast to the 13 children without weight loss, substantial weight loss in 31 children led to a significant (P = 0.007) increase in obestatin and to a significant (P < 0.05) decrease in leptin and insulin concentrations, while ghrelin concentrations did not change significantly. Children with substantial weight loss demonstrated significantly (P = 0.009) lower obestatin and a tendency (P = 0.064) to higher ghrelin concentrations at baseline. Changes in insulin were not related to changes in ghrelin or obestatin.

CONCLUSION

The increase in obestatin and the decrease in ghrelin in obese children point towards an adaptation process of weight status. Weight reduction due to a long-term lifestyle intervention resulted in an increase in obestatin levels.

Central and peripheral roles of ghrelin on glucose homeostasis

Ghrelin, an acylated 28-amino-acid peptide, is an endogenous ligand of the growth hormone secretagogue type 1a (GHS-R1a). Ghrelin is best known for its hypothalamic actions on growth hormone-releasing hormone neurons and neuropeptide Y/agouti-related peptide neurons; however, ghrelin affects multiple organ systems and the complexity of its functions is only now being realized. Although ghrelin is mainly produced in the stomach, it is also produced in low levels by the hypothalamus and by most peripheral tissues. GHS-R1a is expressed predominantly in the anterior pituitary gland, at lower levels in the brain including hypothalamic neurons that regulate feeding behavior and glucose sensing, and at even lower levels in the pancreas. A reciprocal relationship exists between ghrelin and insulin, suggesting that ghrelin regulates glucose homeostasis. Ablation of ghrelin in mice increases glucose-induced insulin secretion, and improves peripheral insulin sensitivity. This review focuses on the newly emerging role of ghrelin in glucose homeostasis and exploration of whether ghrelin is a potential therapeutic target for diabetes.